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Home » Security Advisories» FreeBSD » Security compromise from ppp

Security compromise from ppp

The ppp program does not properly manage user privileges, allowing users to run any program with root privileges.

  • Vendor: FreeBSD
  • Vendor ID: SA-96:15
  • Date: July 04, 1996


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=====================================================================
FreeBSD-SA-96:15 Security Advisory
FreeBSD, Inc.

Topic: security compromise from ppp

Category: core
Module: ppp
Announced: 1996-07-04
Affects: FreeBSD 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected: 2.1-stable and 2.2-current as of 1996-06-10
FreeBSD only: unknown

Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:15/

=====================================================================

I. Background

FreeBSD ships a userland ppp program that can be used by users
to set up ppp connections.
This program is also known as ijppp.
The ppp program has a vulnerability that allows any user to run
commands under root privileges.

II. Problem Description

The ppp program does not properly manage user privileges, allowing
users to run any program with root privileges.

III. Impact

This vulnerability can only be exploited by users with a valid
account on the local system to easily obtain superuser access.

IV. Workaround

One may simply disable the setuid bit on all copies of the ppp
program. This will close the vulnerability but will only allow
the superuser to set up ppp connections.

As root, execute the commands:

# chmod 555 /usr/sbin/ppp

then verify that the setuid permissions of the files have been
removed. The permissions array should read "-r-xr-xr-x" as
shown here:

# ls -l /usr/sbin/ppp
-r-xr-xr-x 1 root bin 86016 Nov 16 1995 /usr/sbin/ppp

V. Solution

Patches are available which eliminate this vulnerability.
The following patch should be applied to the system sources and
ppp should be rebuilt and reinstalled. The first patch is against
the FreeBSD 2.1 and FreeBSD-stable source tree. The second patch
is for FreeBSD-current (version before 1996-06-10).

Apply the patch, then (being superuser):
# cd /usr/src/usr.sbin/ppp
# make depend
# make all
# make install

Index: command.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/command.c,v
retrieving revision 1.5.4.3
retrieving revision 1.5.4.4
diff -u -r1.5.4.3 -r1.5.4.4
--- command.c 1996/02/05 17:02:52 1.5.4.3
+++ command.c 1996/06/10 09:41:49 1.5.4.4
@@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
- * $Id: command.c,v 1.5.4.3 1996/02/05 17:02:52 dfr Exp $
+ * $Id: command.c,v 1.5.4.4 1996/06/10 09:41:49 ache Exp $
*
*/
#include
@@ -187,9 +187,14 @@
* We are running setuid, we should change to
* real user for avoiding security problems.
*/
- setgid( getgid() );
- setuid( getuid() );
-
+ if (setgid(getgid()) < 0) {
+ perror("setgid");
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ perror("setuid");
+ exit(1);
+ }
TtyOldMode();
if(argc > 0)
execvp(argv[0], argv);
Index: chat.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/chat.c,v
retrieving revision 1.4.4.1
retrieving revision 1.4.4.2
diff -u -r1.4.4.1 -r1.4.4.2
--- chat.c 1995/10/06 11:24:31 1.4.4.1
+++ chat.c 1996/06/10 09:41:45 1.4.4.2
@@ -18,7 +18,7 @@
* Columbus, OH 43221
* (614)451-1883
*
- * $Id: chat.c,v 1.4.4.1 1995/10/06 11:24:31 davidg Exp $
+ * $Id: chat.c,v 1.4.4.2 1996/06/10 09:41:45 ache Exp $
*
* TODO:
* o Support more UUCP compatible control sequences.
@@ -331,6 +331,15 @@
nb = open("/dev/tty", O_RDWR);
dup2(nb, 0);
LogPrintf(LOG_CHAT, "exec: %s\n", command);
+ /* switch back to original privileges */
+ if (setgid(getgid()) < 0) {
+ LogPrintf(LOG_CHAT, "setgid: %s\n", strerror(errno));
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ LogPrintf(LOG_CHAT, "setuid: %s\n", strerror(errno));
+ exit(1);
+ }
pid = execvp(command, vector);
LogPrintf(LOG_CHAT, "execvp failed for (%d/%d): %s\n", pid, errno, command);
exit(127);


Patch for FreeBSd-current before 1996-06-10:


Index: command.c
=====================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/command.c,v
retrieving revision 1.17
retrieving revision 1.18
diff -u -r1.17 -r1.18
--- command.c 1996/05/11 20:48:22 1.17
+++ command.c 1996/06/09 20:40:58 1.18
@@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
- * $Id: command.c,v 1.17 1996/05/11 20:48:22 phk Exp $
+ * $Id: command.c,v 1.18 1996/06/09 20:40:58 ache Exp $
*
*/
#include
@@ -190,9 +190,14 @@
* We are running setuid, we should change to
* real user for avoiding security problems.
*/
- setgid( getgid() );
- setuid( getuid() );
-
+ if (setgid(getgid()) < 0) {
+ perror("setgid");
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ perror("setuid");
+ exit(1);
+ }
TtyOldMode();
if(argc > 0)
execvp(argv[0], argv);
Index: chat.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/chat.c,v
retrieving revision 1.10
retrieving revision 1.11
diff -u -r1.10 -r1.11
--- chat.c 1996/05/11 20:48:20 1.10
+++ chat.c 1996/06/09 20:40:56 1.11
@@ -18,7 +18,7 @@
* Columbus, OH 43221
* (614)451-1883
*
- * $Id: chat.c,v 1.10 1996/05/11 20:48:20 phk Exp $
+ * $Id: chat.c,v 1.11 1996/06/09 20:40:56 ache Exp $
*
* TODO:
* o Support more UUCP compatible control sequences.
@@ -393,6 +393,15 @@
nb = open("/dev/tty", O_RDWR);
dup2(nb, 0);
LogPrintf(LOG_CHAT_BIT, "exec: %s\n", command);
+ /* switch back to original privileges */
+ if (setgid(getgid()) < 0) {
+ LogPrintf(LOG_CHAT_BIT, "setgid: %s\n", strerror(errno));
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ LogPrintf(LOG_CHAT_BIT, "setuid: %s\n", strerror(errno));
+ exit(1);
+ }
pid = execvp(command, vector);
LogPrintf(LOG_CHAT_BIT, "execvp failed for (%d/%d): %s\n", pid, errno, command);
exit(127);

=====================================================================
FreeBSD, Inc.

Web Site: http://www.freebsd.org/
Confidential contacts: [email protected]
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: [email protected]
Security public discussion: [email protected]

Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=====================================================================

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